ROCHESTER (Minnesota) • Two months after the first Covid-19 vaccines received clearance in the United States, the shots’ efficacy is holding up well in the real world, according to a study among more than 31,000 people immunised in four states.
The report, one of the first large-scale studies to assess how vaccines are performing in practice, used artificial intelligence (AI) software to scan the medical records of early vaccine recipients at Mayo Clinic facilities.
The findings are important because vaccine and drug efficacy in the real world often differs from what is seen in the carefully controlled environment of experimental clinical trials.
Covid-19 infection rates were almost 89 per cent lower in people who received two doses of the Moderna or Pfizer-BioNTech vaccines.
That compares with a matched control group of demographically similar people who lived in the same US postal codes but were not yet immunised.
Those diagnosed with Covid-19 were 60 per cent less likely to be hospitalised if they had been vaccinated, the study found.
“It is very reassuring that we observed a high level of activity,” said co-author Andrew Badley, an infectious disease specialist at the Mayo Clinic in Rochester, Minnesota.
“The efficacy is essentially unchanged from what we saw in the clinical trials.”
The study involving mostly healthcare workers and long-term care residents has not been published, but was posted without an independent review of the findings to research sharing platform OSF Preprints on Wednesday.
However, it offers an indication of what to expect as vaccinations gain steam, with more than 56.1 million doses administered in the US and 181 million given worldwide, according to the Bloomberg Vaccine Tracker.
Covid-19 infection rates were almost this much lower in people who received two doses of the Moderna or Pfizer -BioNTech vaccines.
Researchers were able to perform the study so quickly thanks to the AI software designed by the Cambridge, Massachusetts-based start-up nference, which has been collaborating with the Mayo Clinic since early last year. It has raised US$145 million (S$193 million) in venture financing from the Mayo Clinic and others.
The software can instantly create matched control groups by finding people in the Mayo Clinic health system who are demographically and geographically identical to those who received a certain drug or vaccine.
“It is lightning fast,” said Mr Venky Soundararajan, co-founder of nference and an author of the study. “You can click a button to create the cohort.”
Meanwhile, two Canada-based researchers, Dr Danuta Skowronski and Dr Gaston De Serres, have urged governments to delay administering the second dose of the Pfizer-BioNTech vaccine, which they said had an efficacy of 92.6 per cent after the first dose, as it was not significantly beneficial in the short term.
They cautioned that there may be uncertainty about the duration of protection with a single dose, but said that the administration of the second dose a month after the first provided “little added benefit in the short term”.
“Given the current vaccine shortage, postponement of the second dose is a matter of national security that, if ignored, will certainly result in thousands of Covid-19-related hospitalisations and deaths this winter in the US,” they said.
In its response, Pfizer said that alternative dosing regimens of its vaccine had not been evaluated yet and the decision to do that resided with the health authorities.